Fans of Interracial Romance discussion

I’m trying to write a story that involves her husband (not the hero of the story) having a long distance affair, but I’m really not sure how to present it. I can’t decide how to present how their relationship. Right now I have it as if she loves him and he loves her but he also (low-key) fell in love with the mistress. But it’s not taking off in my head, and I’m really not sure if that’s the best way to present it. I just need ideas to bounce between here because I’m stuck. I’ve considered a possible small abusive toll, but I don’t know. Also, she’s pregnant.